We wish to define the pathogenesis of ulcerative colitis, in particular, the mechanism of colonic mucosal injury. The objectives are: (1) to isolate colonic mucosal bound antibody or immune complexes and define their specificity and role in the disease process, followed by use of the antibody to identify putative antigen(s), and (2) to study the secretory IgA status of colonic mucosa in ulcerative colitis and its role in pathogenesis of the disease. By acid elution techniques we have isolated a specific IgG antibody bound to the colonic mucosa of patients with ulcerative colitis. Initial experiments indicate that this colitis colon bound antibody (CCA) is of low purity and contained fragmented IgG. We have improved the extraction procedure using protease inhibitors and different elution techniques and purified the intact IgG by protein-A Sephorose 4B affinity chromatography. Purified intact CCA-IgG specifically recognizes mucosal extracts of colon from patients with ulcerative colitis. Larger amounts of purified antibody will be isolated and using affinity chromatography with CCA-IgG the protein(s) in the mucosal extract specifically binding to the CCA-IgG will be isolated and characterized. Several extraction procedures will be performed to prepare the mucosal extracts. In addition, cross-reactivity to bacterial antigens will be examined with fecal anaerobes and aerobes. The role of the antibody on antibody-dependent cell-mediated colonic epithelial cytolysis will be investigated. Using antibody dependent microcytotoxicity assay system, we demonstrated a specific serum antibody in patients with ulcerative colitis. This antibody recognizes an "antigen" in an established human colon epithelial cancer cell line. This recognition will be further investigated with other human colon cancer cell lines, noncolon cancer cell lines and other human cell lines to established the specificity. Using purified CCA-IgG similar ADCC activity will be examined. The secretory IgA system in colonic mucosa will be quantitated by analytical methods including double antibody and solid phase radioimmunoassays which are being used to quantitate the salivary proteins of patients with inflammatory bowel disease.